The present invention relates to an improvement in a roll tarp covering device employed by truck trailers with an open top configuration used for loading and unloading of materials being transported. More specifically, a device which secures a flexible cover for these types of trailers and protects the materials contained therein from the elements and prevents such material from flying out of the open top trailer while the vehicle is in motion.
In the past, trailers pulled by large trucks or farm equipment have proven to be a desirable method by which a variety of materials can be transported over both long and short distances. For ease in loading and unloading materials these trailers were designed with an open top. This configuration allows certain materials such as sand, gravel, grain and various other types of farm produce, to be poured or dropped into the bin of the trailer by means of commonly used collecting equipment such as augers.
An inherent problem associated with this type of trailer occurs when the truck and trailer are moving at high speeds on the highway during transport. The materials being transported can fly out of the top of the trailer while it is in motion, causing loss of the material and potential damage to other vehicles on the road. Additionally, some materials, especially grains and other produce, must be protected from inclement weather conditions such as rain, snow or hail, which could damage the product by entering the open top of the trailer during transport.
Truck and trailer combinations as described above are generally operated by a single driver. A complicated covering device that requires two or more persons to employ is simply not practical for use by a driver traveling alone. Thus, a suitable covering device must be simple, as well as effective, in order to be of use.
Prior art illustrates various devices which have been used to cover the open portion of the trailer. U.S. Pat. Nos. 3,397,009, 3,498,666, 3,854,770 and 4,030,780 all employ a tarpaulin which is attached on one edge to a tube-like shaft or roll tube, which is in turn mounted to the upper edge of one side of the trailer at its forward most and rearmost points. These are commonly known as roll tarpaulins. When the device is not in use, the tarpaulin is rolled around the shaft and stored on the edge of the trailer to which the tarpaulin is permanently attached. When employed, commonly with a manual crank and handle, the shaft is rolled across the open top of the trailer, unrolling the tarpaulin to cover the top of the trailer. When the shaft apparatus reaches the opposite side of the trailer, the tarpaulin is completely unrolled, and provides a cover for the top of the trailer. The shaft is then fastened to the opposite edge of the trailer at various points, commonly the forward most and rearmost points. Thus, the fully unrolled tarpaulin is secured to the edge of the trailer along one side and at the front and back corners on the other side.
The prior art designs employ various methods of rolling and unrolling the tarpaulin and attaching to the tarpaulin to the trailer. However, all of these designs share a common flaw. This flaw is a result of the tarpaulin only being connected to the top of the trailer at the two corners on the opposite side, thus the shaft to which the tarpaulin is attached can bend upwards when the vehicle is in motion. This allows air to enter the enclosed trailer and push the tarpaulin upward, preventing a tight fit of the tarpaulin over the top of the trailer. This problem can also allow rain, snow or other elements, to enter the trailer, and in extreme situations, destroy the tarpaulin and shaft. Further complicating this problem is the fact that often trucks are heaped full and will have different sizes of peaks from the contents along the length of the truck box. This will cause the tension on the tarpaulin and shaft to vary along its length. For example if a large load of grain is placed in the middle of the truck box creating a peak of grain which rises above the walls of the box, then the tarp is subsequently unrolled over this pile with the forward and rearward ends of the tarp being fastened at a given tension, the peak of grain will cause the tarp to be tighter about this portion. Thus, the shaft will often bow in the middle. One solution has been the use of stronger shafts, however, this increases weight and also the cost of the tarpaulin. A second solution used in solving this problem has been to supply straps at various intervals along the shaft. Along with these straps, latches are placed on the sides of the truck box these latches are aligned with the straps. In this configuration, the truck operator must manually connect the straps to the latches and tighten the straps to draw the tarpaulin into a taught position over the truck box. In order to roll the tarp open, the operator must then exit the truck and unlatch the straps.
A still further solution has been to provide the edge of the truck box with a lip. When the tarp is completely unrolled, the shaft travels under this lip so that subsequent turns of the shaft draws it under the lip. The problem with this design is that it does not account for various load sizes along the length of the truck box. Thus, an even tension cannot be placed on the tarp at various points.
Recently, many truck boxes have been equipped with electric tarpaulins that may be rolled and unrolled conveniently from the cab using an electric motor commonly placed at one end of the shaft. Electric tarpaulins also suffer from the same problems as encountered on manual roll tarpaulins as described above. Further, the use of hold down straps with electric tarpaulins is self defeating as the operator must exit the cab of the truck in order to secure an unrolled tarp or to release a tarp prior to uncovering the truck.
Pursuant to the foregoing discussion, it can be seen that it would be desirable to provide a method to cover the top of an open top trailer which would provide a tight fit, preventing air and rain from entering the trailer while it is in motion. It would also be desirable to provide a means of securing a roll tarp in a covered position without manual operation of latches or straps. Finally, it would be desirable to provide a means of holding the roll tarp shaft at various intervals. This means would need to firmly hold the tarpaulin shaft, yet it must account for bowing in the shaft caused by an uneven load while still holding the shaft at various points with sufficient tension.
This is accomplished by means of cleats employed at various points along the edge of the trailer to which the shaft is moved in deploying the tarpaulin. These cleats provide additional points to which the tarpaulin and shaft are attached, preventing large bends in the shaft yet allowing for various tensions along the length of the shaft caused by uneven loading of the truck box.